Field of the Invention
The present invention relates to an image combining apparatus, an image combining system, an image combining method, and a storage medium for a program, which are suitable for use for a high dynamic range function, in particular.
Description of the Related Art
In recent years, a number of digital cameras capable of combining a plurality of images and recording a combined image have been commercialized as image pickup apparatus. Of the image pickup apparatus, there have been known image pickup apparatus having a function of combining images captured at exposures that are lower and higher, respectively, than an exposure at which a brightness of a subject is appropriate to improve halation and noise in a dark part. Such function is referred to as “high dynamic range (HDR) function”.
In general, a dynamic range of an image pickup element is narrower than a dynamic range in nature, and when an image is captured in a backlit scene, for example, the halation may appear. When an image is captured with a lower exposure, the captured image becomes dark as a whole, with the result that the halation may be suppressed, but an impression of noise in the dark part is increased. On the other hand, when an image is captured with a higher exposure, the captured image becomes bright as a whole, with the result that the halation appears, but the impression of noise in the dark part is improved. According to the HDR function, a plurality of images, such as a low exposure image and a high exposure image, may be used for combining with the low exposure image being weighted in a bright region (halation or the like) and, on the contrary, the high exposure image being weighted in a dark region to improve the halation and the impression of noise in the dark part.
Moreover, not only the above-mentioned two images: the low exposure image and the high exposure image, but also an image at a higher exposure and an image at a lower exposure may be used for combining to further improve the halation and noise. In other words, a larger number of images at different exposures may be combined to obtain a combined image having a higher dynamic range. In Japanese Patent Application Laid-Open No. 2008-277896, there is disclosed a technology in which the low exposure image and the high exposure image, which is selected from the plurality of high exposure images, are combined to obtain the combined image having the high dynamic range.